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Origin of Species Revisited: Geographical distribution

Chapters Eleven and Twelve

In which Darwin demonstrates the importance of geographical barriers and climate change to explain the distribution of life as we see it today

Penguins are charming birds with between 17 and 20 species, depending on which classification is used. They take a variety of forms, ranging from the statuesque emperor found in the Antarctic, to the fairy penguin of Australia, just 1/20th its weight. Other penguins live in New Zealand, South Africa, South America and the Galapagos. They cannot fly (although the DNA suggests that albatrosses are among their closest relatives), so how did they reach such scattered places?

The oldest penguin fossils appear shortly after the demise of the dinosaurs around 65 million years ago. This ancestor of all living species lived in southern New Zealand and Marie Byrd Land, Antarctica, which were at that time separated by less than 1500 kilometres. Already the ancestral penguins had almost lost their wings. Fossils and DNA each show that the penguins’ spread matches the advance and retreat of the ice. Starting around 35 million years ago, a series of ice ages made the Antarctic uninhabitable, and the birds retreated northwards as the glacier spread. In addition, icy currents swept some westwards, eastwards and closer to the equator.

After 10 million chilly years, the world warmed, cooled and warmed again, and the birds followed the retreating edge of the ice sheet into the far south. They left behind colonies scattered on cold-water shores across the globe. In the years since then, isolation and the challenges faced by each separate group have led to the diversity of penguins seen …